The invention relates to a motorcycle with what is known as hub steering, and in particular to a front wheel suspension for a motorcycle of this nature.
In standard motorcycles, the steering wheel, which is generally the front wheel, is held in a front fork with the aid of its hub and axle. The wheel can turn due to the fact that the front fork as a whole is arranged so that it can turn with respect to the frame of the motorcycle. The hub merely allows the wheel to rotate about its axle.
Designs are also known in which the wheel can turn with respect to its axle. An example of such designs is shown in French patent 1,000,493. In this known design, the (driven) axle is accommodated in the hub by means of a cardan structure. The wheel, which obviously moves together with the hub, is able to turn freely with respect to the axle. The wheel is steered by means of a steering arm, which is preferably arranged resiliently.
This known design has various drawbacks. Firstly, the cardan suspension is not free from vibration. Secondly, the imaginary line about which the wheel is turned during steering passes straight through the axle, resulting in unsatisfactory motorcycle driving characteristics. In particular, the stability will be inadequate.
American patent U.S. Pat. No. 5,042,609 describes a motorcycle with a turnable hub, the turning axis of the handlebars intersecting the wheel axle. The hub is connected to the frame of the motorcycle by means of a single support arm.
European patent EP 0,432,107 likewise describes a motorcycle with a pivotable hub. This hub, the axle of which is fixedly connected to the frame of the motorcycle, allows the wheel, which is arranged so that it can rotate about the hub, to turn. In connection with this hub, the said patent notes that the axle may be arranged in front of the turning axis of the handlebars, in such a manner that the axis of rotation of the wheel and the turning axis of the handlebars do not intersect one another. This known hub is connected to the frame of the motorcycle by means of a single pair of support arms. A steering rod connects the turnable part of the hub to the handlebars.
A structure of this nature, with a single pair of support arms, has the drawback of being relatively unstable. The support arms can become twisted relatively easily under the influence of transverse forces, and this affects the position of the front wheel and therefore the stability of the motorcycle.
It is noted that U.S. Pat. No. 4,721,179 discloses a motorcycle in which the front wheel is supported by an upper and lower swing arm, in which lines connecting the front and rear upper and lower pivot point intersect one another at a point which lies above the swing arms. However, U.S. Pat. No. 4,721,179 does not relate to a motorcycle having hub steering but to a motorcycle having axial pivot steering. During steering the axle, the hub and the front wheel are turned around ball joints as one unit with respect to the swing arms. With this type of steering it is not possible to achieve the same advantageous change in steering sensitivity during inward or outward springing like with the present invention described below. Furthermore the motorcycle according to U.S. Pat. No. 4,721,179 also does have the disadvantageous bump steering effect.
GB-A-833 741 discloses a motorcycle having hub steering. The hub steering comprises a front wheel axle fixedly held between brackets, the axle holding a king pin onto which a hub body is pivoted. The hub body supports roller bearings on which the front wheel can rotate. The brackets are pivotably connected to two pairs of upper and lower links, one of which is connected to a shock absorber, thus providing a parallelogram type suspension for the front wheel. All of the links are of equal length, and the front lower and upper pivot points lie in a straight vertical line above one another. The rear lower and upper pivot points also lie in a straight vertical line above one another. Furthermore the king pin around which the hub body can turn intersects the centre axis of the axle.
A drawback of the hub steering according to GB-A-833 741 is that its steering sensitivity is poor and unfavourable. The feeling of control over the steering is bad. There is a very disadvantageous bump steering effect. The distance between the turning axis of the hub body and the centre axis of the axle is zero, resulting in the front wheel having no castor. This also makes the motorcycle unstable.
The object of the invention is to eliminate the above and other drawbacks of the prior art and to provide a motorcycle which allows what is known as hub steering with considerably improved driving characteristics. Furthermore, the invention aims to provide a motorcycle with improved stability.
According to the invention this object is achieved by a motorcycle having hub steering, comprising a frame, a front wheel, a rear wheel and an engine, in which a front line which joins the lower and upper front pivot points, and a rear line which joins the lower and upper rear pivot points, intersect one another at a point which lies above the support arms, in which the turning axis and the centre axis of the axle are situated at a distance from one another, and in which there is a resilient steering connection between handle bars and the front wheel. By providing two sets of upper and lower support arms, preferably above and approximately parallel to the first support arms, it is possible to achieve greater stability of the motorcycle. Designing the support arms in such a manner that the pivot points do not lie on parallel lines, but rather on intersecting lines, results in a highly advantageous steering sensitivity during compression. The distance between the turning axis of the hub body and the centre axis of the axle provides for an advantageous castor. During inward springing with which the front wheel moves upwardly with respect to the motor frame, the specific positions of the pivot points with respect to each other, in combination with the distance between the turning axis of the hub body and the centre axis of the axle, results in a specific path of change of the angle of the turning axis in combination with the amount of castor. That is to say the steering sensitivity changes during inward springing such, that it will be more easy to steer the motorcycle.